The present invention relates to a driving method for driving a chiral smectic liquid crystal device, particularly of an electrode matrix-type, and a liquid crystal apparatus including the chiral smectic liquid crystal device.
A liquid crystal device showing bistability has been proposed by Clark and Lagerwall in U.S. Pat. No. 4,367,924, Japanese Laid-Open Patent Application (JP-A) No. 56-107216, etc. As the bistable liquid crystal, a ferroelectric liquid crystal showing chiral smectic C phase (SmC*) or H phase (SmH*) is generally used. The ferroelectric liquid crystal assumes either a first optically stable state or a second optically stable state in response to an electric field applied thereto and retains the resultant state in the absence of an electric field, thus showing a bistability. Further, the ferroelectric liquid crystal quickly responds to a change in electric field, and thus the ferroelectric liquid crystal device is expected to be widely used in the field of a high-speed and memory-type display apparatus, etc.
The ferroelectric liquid crystal device generally has an electrode matrix wherein a pair of substrates are each provided with a group of stripe-shaped electrodes intersecting with each other at right angles to form a multiplicity of pixels at each intersection of the electrodes, and is driven by, e.g., driving methods described in JP-A Nos. 59-193426, 59-193427, 60-156046, 60-156047, etc.
In the above-described conventional driving methods, an electric field required for providing either the first optically stable state or the second optically stable state is decreased with an increasing temperature, thus changing a drive waveform depending on a temperature in order to maintain good display states.
The conventional driving methods, however, have been accompanied with problems in some cases when the liquid crystal device used is driven at high temperature.
More specifically, if a pulse width of the drive waveform is shortened at a high temperature, the liquid crystal device is driven at a high voltage, thus leading to a shorter response time (higher response speed) of the liquid crystal used and a larger amplitude of the drive waveform. As a result, a power consumption of the liquid crystal apparatus is increased. Further, the driving method using the higher voltage is liable to cause heat evolution or generation, thus resulting in a temperature unevenness (irregularity in temperature distribution) in a display region of the liquid crystal device.
On the other hand, if the driving voltage is lowered to suppress heat evolution, a resultant drive margin is decreased or narrowed.
An object of the present invention is to provide a driving method for a liquid crystal device having solved the above-mentioned problems and capable of providing a larger (wider) drive margin at low power consumption irrespective of temperature change while keeping good image qualities.
Another object of the present invention is to provide a liquid crystal apparatus including the liquid crystal device.
According to the present invention, there is provided a driving method for a liquid crystal device of the type comprising a pair of substrates and a chiral smectic liquid crystal disposed between the substrates so as to form at least one pixel, the driving method comprising:
applying a signal waveform to a selected pixel, wherein
the signal waveform comprises a clear pulse for placing the liquid crystal in a first state and a writing pulse subsequent to the clear pulse for selectively placing the liquid crystal in a second state depending on input data, and
the writing pulse comprises a higher voltage portion and a pair of lower voltage portions sandwiching the higher voltage portion.
According to the present invention, there is also provided a driving method for a liquid crystal device of the type comprising a pair of substrates and a chiral smectic liquid crystal disposed between the substrates so as to form at least one pixel, the driving method comprising:
applying a signal waveform, changed depending on a temperature of the liquid crystal device, to a selected pixel, wherein
the signal waveform comprises a waveform at a high temperature including a clear pulse for placing the liquid crystal in a first state and a writing pulse subsequent to the clear pulse for selectively placing the liquid crystal in a second state depending on input data, and
the writing pulse comprises a higher voltage portion and a pair of lower voltage portions sandwiching the higher voltage portion.
According to the present invention, there is further provided a liquid crystal apparatus, comprising:
a liquid crystal device comprising a pair of substrates and a chiral smectic liquid crystal disposed between the substrates so as to form at least one pixel, and
signal waveform application means for applying a signal waveform to a selected pixel, wherein
the signal waveform comprises a clear pulse for placing the liquid crystal in a first state and a writing pulse subsequent to the clear pulse for selectively placing the liquid crystal in a second state depending on input data, and
the writing pulse comprises a higher voltage portion and a pair of lower voltage portions sandwiching the higher voltage portion.
According to the present invention, there is still further provided a liquid crystal apparatus, comprising:
a liquid crystal device comprising a pair of substrates and a chiral smectic liquid crystal disposed between the substrates so as to form at least one pixel, and
signal waveform application means applying a signal waveform, changed depending on a temperature of the liquid crystal device, to a selected pixel, wherein
the signal waveform comprises a waveform at a high temperature including a clear pulse for placing the liquid crystal in a first state and a writing pulse subsequent to the clear pulse for selectively placing the liquid crystal in a second state depending on input data, and
the writing pulse comprises a higher voltage portion and a pair of lower voltage portions sandwiching the higher voltage portion.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.